(Bloomberg) -- President Joe Biden’s top adviser on Russia at the National Security Council is leaving his post as the US continues to grapple with the Kremlin’s war in Ukraine.

Eric Green, special assistant to the president and the NSC’s senior director for Russia and Central Asia, is leaving the post as he prepares to retire from the foreign service after more than three decades.

“Eric has been absolutely central to our efforts here at the NSC in leading the charge to hold Russia accountable and support Ukraine. His insights & actions have proven pivotal time and again, and I’m immensely grateful for his service,” said White House National Security Adviser Jake Sullivan in a statement.

At the White House, Green led the directorate that covers Russia and Central Asia, and coordinated policy with the NSC’s leadership, its Europe team and agencies across the government. He helped prepare Biden for his 2021 summit with Russian President Vladimir Putin in Geneva and has played a central role in developing the administration’s response to Putin’s invasion of Ukraine. 

Green had already extended his detail from the State Department once at the White House’s request, according to a White House official.

Biden said during his State of the Union address Tuesday night that Russia’s invasion of Ukraine was “a test for the ages” that the US and its NATO allies had passed. He vowed again to stand with Ukrainian President Volodymyr Zelenskiy as long as needed.

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